Engine freshen-up – what to check

 In Engine General, MGA-MGB, Midget

An engine freshen-up is a term that means different things to different people.

In the context of the following I have taken it to be replacing the rings and bearing shells and attending to other items on an as-required basis. Taking this approach, the following points may be useful in considering other components:

Oil pump or rotor kit – what was the oil pressure like before stripping the engine? If over 30 psi at idle (about 700 – 800 RPM) when hot, then the pump should be OK.

Cam followers – the Achilles heel of the B series in particular – is there any sign of pitting? If there is (even slight), replace them as they will wear out the camshaft quickly. I strongly advise against refacing followers, as they are very soft once the hardened skin has been penetrated – furthermore the cost of refacing is only marginally less than new followers.

Camshaft – If pitting in the followers is bad, check the camshaft for wear and get reground if necessary. The lift of each lobe of a standard MGA or MGB cam should be 0.268”. For the Midget the valve lift when set to the running clearance is listed as 0.312”, which equates to 0.250” cam lift after allowing for the rocker ratio. The XPAG engine of T-types are particularly prone to cam lobe wear, To measure cam lift, measure the largest “diameter” of the lobe – from cam peak to the other side – then subtract the base circle diameter (measure at right angles to the first measurement). Accept wear less than 3 thou. Wear will be evident from varying lifts between lobes.

Timing chain and tensioner – renew unless perfect – they are cheap.

Rocker shaft and bushes – look for wear on the shaft under the rockers (slide them to one side, look at the bottom of the shaft.) If the shaft is worn, renew it. Slide the rockers along the shaft to an unworn bush and check for slackness. Renew the bushes if necessary (they will need fitting and reaming to size).

Unleaded conversion – If your head has not been fitted with hardened exhaust seats, I’d strongly recommend doing it now while the head is off. It is relatively inexpensive so the pay-back period due to not having to use additive is not that long. On top of that, there is less hassle and the seats give added protection to the head from cracking in the event of a valve burning out. It pays to renew the exhaust valves when doing this job, they are reasonably priced.

Ring gear – If your car doesn’t have a pre-engage starter, then check the ring gear for wear. Pre-engage starters were introduced in 1968 for the MGB only along with the full synchromesh gearbox. The Midget continued with the inertia starter. (Note that a first registered 1968 car could have been made in 1967 as there is shipping and showroom time to add to the manufacture date)

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